Levelwind, Notice how the "stones" sit.
I like the one the middle too.
Some strange things. There are too many coincidences in terms of shape and internal consistency on images from NASA as cited similar forms here on Earth, that the coincidence can not be the case.
http://pancam.astro.cornell.edu/pancam_instrument/images/True/Sol041A_P2530_1_True_RAD.jpg